Escape to Ferality: The Endoferal Origin of Weedy Rice from Crop Rice through De-Domestication

Abstract

Domestication is the hallmark of evolution and civilization and harnesses biodiversity through selection for specific traits. In regions where domesticated lines are grown near wild relatives, congeneric sources of aggressive weedy genotypes cause major economic losses. Thus, the origins of weedy genotypes where no congeneric species occur raise questions regarding management effectiveness and evolutionary mechanisms responsible for weedy population success. Since eradication in the 1970s, California growers avoided weedy rice through continuous flood culture and zero-tolerance guidelines, preventing the import, presence, and movement of weedy seeds. In 2003, after decades of no reported presence in California, a weedy rice population was confirmed in dry-seeded fields. Our objectives were to identify the origins and establishment of this population and pinpoint possible phenotypes involved. We show that California weedy rice is derived from a different genetic source among a broad range of genome Oryzas and is most recently diverged from O. sativa temperate japonica cultivated in California. In contrast, other weedy rice ecotypes in North America (Southern US) originate from weedy genotypes from China near wild Oryza, and are derived through existing crop-wild relative crosses. Analyses of morphological data show that California weedy rice subgroups have phenotypes like medium-grain or gourmet cultivars, but have colored pericarp, seed shattering, and awns like wild relatives, suggesting that reversion to non-domestic or wild-like traits can occur following domestication, despite apparent fixation of domestication alleles. Additionally, these results indicate that preventive methods focused on incoming weed sources through contamination may miss burgeoning weedy genotypes that rapidly adapt, establish, and proliferate. Investigating the common and unique evolutionary mechanisms underlying global weed origins and subsequent interactions with crop relatives sheds light on how weeds evolve and addresses broader questions regarding the stability of selection during domestication and crop improvement.

Contrasting patterns of variation in weedy traits and unique crop features in divergent populations of US weedy rice (Oryza sativa sp.) in Arkansas and California

“…Weedy rices can derive from crops and differ from their closest wild or crop relatives in morphological traits. In general, weedy rices are more similar to wild relatives in traits such as awnedness, seed shattering (dispersal), rapid growth rate and plant height, tillering, protracted flowering time (heading date), pericarp (bran) pigmentation, seed longevity and dormancy . Weedy traits increase competitive abilities in weeds .…”

“…De ‐ domestication – the reversion of crop populations to feral weeds – plays an important role in the evolution of weeds as agroecological pests, including weedy rice . Being conspecific with cultivated rice makes control of weedy rice difficult because morphological and physiological traits are shared with the crop.…”

Genetic variation and possible origins of weedy rice found in California

“…The increasing spread of weedy rice in California and the recent report of weedy rice originating from cultivated California rice varieties (Kanapeckas et al, 2016) raised questions about the origin of California weedy rice and its management. For this reason, we conducted a genetic study to understand the relationships between existing weedy rice in California and to investigate their possible origins.…”

“…In 2003, however, weedy rice of a single biotype was reported in a dry-seeded rice field (Kanapeckas et al, 2016). Since then, weedy rice has been identified in at least 60 fields and on over 4,050 ha in 2016(Whitney Brim-DeForest, personal communication, February 5, 2018.…”

“…Since then, weedy rice has been identified in at least 60 fields and on over 4,050 ha in 2016(Whitney Brim-DeForest, personal communication, February 5, 2018. While weedy rice in the southern United States has been well-characterized (Li et al, 2017;Londo & Schaal, 2007;, weedy rice in California is a recent and growing problem with previous studies limited to one or two biotypes (Kanapeckas et al, 2017(Kanapeckas et al, ,2016Londo & Schaal, 2007). It is unclear whether California weedy rice is derived from the weedy rice present in the southern United States, from cultivated rice inside or outside of California, from Asian wild rice, or from hybridization of any of these groups.…”